Overrunning or one way clutches are commonly known today and there are various types of such clutch assemblies in use. Overrunning clutch assemblies are designed to have many different structures, including ratchet-type clutches and traction/locking clutches, such as a roller ramp clutch or sprag clutch. Traction-type clutches are generally limited in their applicability if high torque delivery is a design requisite. Therefore, ratchet-type clutches are preferred in instances where increased torque capacity is needed for transmissions containing one way clutch assemblies. Such rachet-type clutch assemblies make use of pawls carried by a drive member, which are designed to engage with notches, commonly located in a driven member. The capacity to carry increasing torque amounts and eliminate the potential for clutch backlash variously depends upon the number of pawls engaged with notches at any given point in time and the overall dimensions of the driven and drive members.
A typical ratchet-type clutch assembly is shown in U.S. Pat. No. 5,853,073. The '073 patent discloses a radial ratchet clutch assembly having an inner radial race juxtaposed with an outer radial race. The outer radial race includes a plurality of pockets having pawls positioned in the pockets for engagement with notches located in the inner radial race. The pawls are designed to have a center of mass such that when the clutch rotates, centrifugal force acts upon the center of mass and causes the pawls to move into an engaged position with the notches of the inner radial race. Other embodiments in the '073 patent make use of spring members to tilt or force the pawls toward engagement with the notches.
Radial ratchet clutch assemblies such as that disclosed in the '073 patent can be designed for heavy torque transfer and are commonly very reliable. However, when design applications call for a lightweight clutch assembly or clutch assembly of minimized axial dimensions that remains capable of high torque transfer, radial ratchet one way clutches such as that shown in the '073 patent are commonly unsuitable.
One solution has led to the design of a planar ratchet assembly, such as that shown in U.S. Pat. No. 5,070,978. The '978 patent discloses a planar ratchet one way clutch having a planar drive member and a planar driven member positioned in close proximity to the planar drive member. A series of pockets is incorporated in the driven face and a plurality of cooperating pawls are positioned in the drive face. When the drive member is rotated in a desired direction by a suitable source of power, only one of the plurality of pawls will engage with only one of the plurality of pockets to impart drive forces to the driven member. The pawls of the '978 patent are designed to have a narrow cross-section so as to provide for easy movement from a position of non-engagement to a position of engagement with a low moment of inertia. The pawl members have torsion springs disposed in recesses centrally located in the pawl which act to outwardly displace the pawl for engagement with the pocket of the driven member. However, planar ratchet assemblies such as that disclosed in the '978 patent have encountered problems when heavy torsional loading is applied, such as eccentric deformation of the drive and/or driven plates and a common failure due to the buckling of the pawls.
Another embodiment of a planar ratchet one way clutch assembly is shown in U.S. Pat. No. 5,597,057. The '057 patent again discloses a one way clutch apparatus having a planar driving member with a plurality of recesses and biasing members with pawls of thin cross-section are disposed in the recesses. A driven member having a plurality of engaging notches is juxtaposed with the driving member. The pawls are spring loaded to press engagement of the pawls into the notches of the driven member. Again, problems similar to these discussed earlier with regard to the '978 patent have been encountered with clutches of the type of the '057 patent when heavy torsional loading is applied.
Such planar clutches have small pawls, commonly of a generalized rectangular shape that are long and thin and are commonly designed so that only one pawl is engaged at a time. The use of such long thin pawls allows for the placement of an increased number of pawls and notches in the clutch, thereby reducing the potential for backlash in the clutch. However, because only one pawl is commonly available to carry the entire load, the torque capacity of the prior art planar clutches does not meet desired levels. Loading on a single thin pawl will cause high eccentric loads on the drive plate and driven plate that wear down the clutch. Further, the thinness of the pawl will increase the potential for the pawl to buckle under high static loads.
Thus, it is an object of the invention to provide for a one way planar ratchet clutch capable of carrying and transmitting heavy torque loads.
Yet another objective of the present invention is to provide for a planar ratchet one way clutch, wherein the components are minimized in size without impairing the ability of the clutch to transmit heavy torque loads without incurring eccentric deformation and failure or buckling of the pawls.
Yet another object of the present invention is to provide a planar ratchet one way clutch, wherein at least one of the planar juxtaposed driven members has a flat backing surface capable of utilization as a backing plate for a friction plate of the clutch.
Yet another objective of the present invention is to provide for compact pawls having a cross-section, wherein high torque loading on the pawls will not cause the pawl to buckle.